The invention relates to a pressure booster for increasing the pressure of a hydraulic fluid by means of a pressure gas, as indicated in the introduction of claim 1.
A booster of this type can be found on the market, where the check valve is operated by an end portion of a rod which extends through the main piston from near an end portion thereof which is influenced by low-pressure fluid where the rod is arranged to abut against a portion of the housing. The shut-off valve comprises a valve piston which is slidably mounted in the housing and which is influenced by the low-pressure fluid at the same time as the main piston is influenced by this pressure. The shut-off valve can thereby be opened and compressed air is supplied to the third cylinder space, thus causing the main piston to be moved and the pressure in the fluid in the second cylinder space increased before the check valve has been moved to its second position. The result of this is that a high-pressure impulse generated by depressing the clutch pedal can be transmitted from the booster to the clutch master cylinder causing a return movement of the master cylinder""s piston and thereby the clutch pedal, which is undesirable.
The main piston must therefore be moved some distance in order to close the check valve after the shut-off valve has been opened. Only after this closure can the pressure in the high-pressure fluid be increased to the desired value. This is disadvantageous if the booster is employed in connection with an operating device for clutches, where the distance which is available for movement of a clutch pedal is limited.
The characteristics of the booster according to the invention are set forth in the characterising features indicated in the claims.